Part of an object having an indentation or curving inwards.
- The graph of the second-degree polynomial function defined by the equation f(x) = ax² is concave upward when the coefficient a has a positive value and concave downward when the coefficient a has a negative value. The figure below shows the function f defined by f(x) = 0.5(x + 4)2 − 3, in which parameter a = 0.5 is positive. Therefore, the graph is concave upward.
- A lune is a plane concave figure that is bounded by two circular arcs with unequal radii.